DESCRIPTION (from applicant's abstract): A large body of evidence supports the hypothesis that CCK is an important element in the neurochemical balance that is thought to be essential for normal nervous system function. Much of the research on the biological actions of CCK have focused on its role in anxiety, cognitive function, analgesia, substance abuse and in the control of feeding. Altered CCK synthesis and/or release could be involved in the pathophysiology or symptomatology of neurological and psychiatric disease. One of the key events in CCK biosynthesis involves the concerted action of specific endoproteolytic enzymes which cleave pro CCK in a strict temporal order to produce CCK 8. The identity of the enzymes responsible for these cleavages in the brain are unknown but some good candidates have been identified in endocrine tumor cells. The experiments detailed in this proposal continue ongoing studies examining the ability of PC 1, PC2, and PC5 alone or in combination to appropriately cleave pro CCK in endocrine cells and extend these investigations to neuronal cells in culture and to transgenic mice in which PC2 has been knocked out by homologous recombination. The short term goal of this research is to understand the mechanism and regulation of the post-translational processing of pro-cholecystokinin (CCK). The long term goal is to understand what role CCK plays in the brain. By understanding the mechanism and regulation of CCK biosynthesis and processing, it may be possible to alter the rate of synthesis and release of CCK to adjust the neurochemical balance in areas like the striatum and provide some relief of symptoms in specific Neurological Diseases such as Parkinson's. This proposal addresses the following specific aims which test the hypothesis that the action of PC 1, PC2 and PC5 either alone or in combination are required to process pro CKK to CCK 8 amide or other biologically active forms in endocrine and neuronal cells: 1. The ability of PC1, PC2 and PC5 to process pro CCK will be studied in endocrine tumor cells, neuroblastoma cells, immortalized hippocampal neurons, neural progenitor cells before and after differentiation. 2. Using purified recombinant pro CCK and synthetic peptides containing specific cleavage sites, the ability of recombinant PC 1,PC2 and PC5 to cleave pro CCK in vitro will be tested. 3. The role of PC2 in pro CCK processing in brain will be extended to intact animals by examining the products of pro CCK processing in PC2 knockout mice.